Ereaders (Kindle, Nook, Kobo, etc.)

Kindle: download the mobi file to your computer, or use the Send To Kindle button above.
All other ereaders: download the epub file to your computer.

Plug the ereader into your computer with a USB cable.

Using the Finder (Mac) or Windows Explorer (Windows), drag and drop the ebook file into the Documents folder on your device. (It may also be called My Documents or My Stuff, depending on your ereader.)

Dropbox

Dropbox is a good way to share your ebooks between desktop, tablet and smartphone. If you see a dropbox button above, click it to load your books into your dropbox folder. Then load the file into your reader application on your device.